Self-locking pneumatic actuators



T. A. OLDFIELD ETAL 3,141,382

, SELF-LOCKING PNEUMATIC ACTUATORS July 21,

Filed Jan. 24, 1963 United States Patent 3,141,382 SELF-LOCKINGPNEUMATIC ACTUATORS Thomas Alfred Oldfield, Allestree, Derby, andRoderick Rudd Carr, Galleywood, near Chelmsford, England,

assignors to The Plessey Company Limited, Ilford,

Essex, England, a British company Filed Jan. 24, 1963, Ser. No. 253,771Claims priority, application Great Britain Feb. 2, 1962 7 Claims. (Cl.91-44) This invention relates to hydraulic or pneumatic actuatorsystems.

In particular the present invention is concerned with actuator systemsincluding a mechanical locking means for looking a ram of the system inone or the other of its rest positions.

It is an object of the present invention to ensure that the lockingmeans is moved to its released position before the main ram is movedfrom the rest position in which the locking means is applied towards itsother rest position.

Another object is to provide a pneumatic actuator with mechanicallocking means which are automatically actuated by the actuating fluidpressure to lock the main ram when it reaches one of its end positionsand to automatically unlock it at the beginning of its return strokefrom said end position while minimizing wear and strain as well as powerrequirements of the locking mechamsm.

According to the present invention there is provided an actuator system,wherein mechanical locking means are provided for locking a ram of theactuator system in one of its end positions, the mechanical lockingmeans being arranged to be automatically moved into its locked positionwhenever the ram moves into said one position, and wherein the fluidpressure used for moving the ram into its other end position is arrangedto effect the unlocking of the mechanical locking means before it causesthe ram to move.

A further aspect of the invention provides an actuator system includinga main ram unit, mechanical means for locking the main ram in one of itsend positions and a second ram which is connected to operate the lockingmeans, the ram of the second ram unit being moved to effect the lockingof the locking means by a fluid pressure under the control of the mainram on attaining said end position, and the second ram having furthercontrol means whereby when moved to unlock the main ram by the admissionof fluid pressure it subsequently causes said fluid pressure to beapplied to the first ram to move it to its other rest position.

Preferably the first valve includes a fluid passageway on the main ramunit ram which is arranged, when the main unit ram is in said oneposition, to line up with ports included to a pressure fluid pathleading to the cylinder of the second ram unit, thereby to complete saidpath to the cylinder.

Conveniently the further valve includes a passageway on the second ramunit ram which is arranged, when the latter is in the position whichunlocks the locking means, to line-up with ports including in a furtherfluid path leading to the cylinder of the main ram unit thereby tocomplete the further fluid path to the main ram unit cylinder.

For a better understanding of the invention to show how the same may becarried into effect reference will now be made to the accompanyingdrawing which is a schematic diagram illustrating a pneumaticallyoperated actuator system incorporating a pneumatically operatedmechanical lock.

The actuator system includes a main ram piston rod 1 connected at oneend to a piston 2 which is movable 7 3,141,382 Patented July 21, 1964"ice within a cylinder 3 by means of high pressure air applied to one orthe other of the sides 2A and 2B of the piston.

The ram rod 1 is connected by a pivoted member 4 to a mechanical lockingmechanism including a baulk rod 5 which is slidable within a suitableguide schematically indicated at 6. The detent or locking element 7 ofthe locking mechanism is constituted by a baulk roller or latch 7 whichis connected via a crank member 8 to one end of a locking rod 9, whoseother end is connected with a piston 10 which is slidable within afurther cylinder 11. The application of high-pressure air to one or theother of the sides 10A and 10B of the piston 10 is controlled by meansof a selector valve unit including a valve member 12 having two lands 13and 14 which is slidable within a valve housing 15, the lands 13 and 14effectively dividing the housing 15 into three separate sections 16, 17and 18. The high-pressure air supply is fed to the interior of thehousing 15 via a suitable supply conduit 19 which connects with a port26 in the housing Wall.

For convenience of explanation it will be presumed that initially thelocking mechanism is in its oil position as is shown in the drawing;that the ram piston 2 is retracted as is shown in the drawing and thatthe ram rod 9 in its extended position as is shown in the drawing. Inaddition it will be assumed that the selector valve 12 is in theposition indicated in the figure. In this position of the valve 12 thehigh-pressure air supply is fed from the conduit 19, via the port 20,the section 17, a port 21 in the housing 15, conduit 22 and a port 23into the interior of the housing 11 so as to hold the piston 10 in theposition shown in the drawing. In addition, the high-pressure air supplycommunicates with the interior of the cylinder 3 by way of the conduit22, a conduit 24, a port 25 in the housing 11, a groove 26 in the ramrod 9, a second port 127 in the housing 11 and a conduit 28 whichconnects via a port 28A with the interior of the ram cylinder 3, thepressure being applied to the piston side 2A so as to hold the rampiston rod 1 in the position shown. At the same time the chamber 16 ofthe selector valve housing is vented to atmosphere via the exhaust duct29 and the non-pressurised side 2B of the ram piston 2 is vented toatmosphere via a port 30 connecting with conduit 31 which communicateswith a port 32 opening into the section 18 of the housing 15 and port 33which vents to the atmosphere.

In order to move the ram rod 1 towards its extended position theselector valve 12 is moved to its other end position so that the land 14moves to the right in the figure of the port 32 and the land 13 moves tothe right of the port 20. With the selector valve in this position theright-hand of the ram cylinder 11 is vented to atmosphere via the port23, the conduit 22, the port 21, the chamber 16 and the vent port 20.The interior of the ram cylinder 3 is vented to atmosphere via theport-28A, the conduit 28, the port 27, the channel 26, the part 25, theconduit 24, the conduit 23, the port 21, the chamber 16 and the port 29to atmosphere, and highpressure air from conduit 19, is fed via theports 20 and 32, the conduit 31 and the port 30 into the ram cylinder 3to exert pressure on the face 2B of the piston 2 to cause the ram pistonrod 1 to move to its extended position. At this stage the branch 37 ofline 31 is blocked by the piston rod 1. The outward movement of the rampiston rod 1 causes the baulk rod 5 to be withdrawn from the path of thelatch 7 until, when the ram 1, 3 is fully extended, the locking element7 is able to move into the path of the rod 5, at the same time a groove,34 provided in the ram rod 1 aligns with two ports 35 and 36 in the ramcylinder 3, thus admitting this position highpressure air via theconduit 31, a branch conduit 37 leading from the conduit 31, the port35', the groove 34, the port 36, conduit 38 and a port 3? into theleft-hand end of the ram cylinder housing 11, to exert pressure againstside ltlA of the piston 10 to move the latter towards the right therebymoving the rod 9 inwardly into its retracted position. The inwardmovement of the rod 9 moves, via the crank 8, the latch 7 into the pathof the baulk rod thereby locking the ram 1, 3 in its extended position.When the locking rod 9 is in its corresponding retracted position, aventing duct 49 lines up with the port 27 so as to maintain the ventingof the interior of the ram cylinder 3 to atmosphere to prevent pressurebuild-up by leakage past the piston 2.

When it is required to return the ram 1, 3 into its retracted positionthe selector valve 12 is returned to the position shown in the drawing.On moving the selector valve the supply of high pressure air into theconduit 31 is cut otT, so that the application of pressure on the sides2B and A of the pistons 2 and 10 is removed. At the same time the side2B of the piston 2 is vented to atmosphere via the port 39, the conduit31, the port 32, the housing section 18 and the port 33. In addition,the side 10A of the piston 10 is vented to atmosphere via the port 39,the conduit 38, the port 36, the groove 34, the port 35, the conduit 37,the conduit 31, the port 32, the chamber section 18 and the port 33.

High pressure air exerts pressure against the piston side 1613 via theport 20, the chamber section 17, the port 21, the conduit 22, and theport 23.

Since the ram 9, at this stage is in its retracted position the groove26 is not aligning with the ports 25 and 27 so that the high pressuresupply cannot be applied via the path previously described into theinterior of the cylinder 3 to exert pressure on the piston side 2A. Inother words, bearing in mind that both sides of the piston 2 arevented-in the manner described-to atmosphere, it will be apparent thatthe ram 1 remains in its retracted position.

On applying the high pressure to the piston side NB the ram rod 9 movesto its extended position, simultaneously withdrawing the latching orlocking element 7 back to the released position shown in the figure.While the element is moved out of the path of the rod 5, the vent 40moves out of alignment with the port 27, and when the element 7 is clearof the path of the rod 5 the groove 26 aligns with the two ports 25 and27 thereby completing the high pressure supply path to the interior ofthe ram cylinder 3 to exert pressure on the piston side 2A. The piston 2is then moved thereby retracting the ram rod 1.

So long as the selector valve is maintained in the position indicated inthe drawing the ram rod 1 is maintained in its retracted position andthe locking mechanism is maintained in its off position.

It will be understood that in a practical form of the above describedsystem many of the conduits would be constituted by ducts or the like inthe walls of the various cylinder housings.

Furthermore, the housing 11 and the housing could be incorporated in acommon valve body.

In a particular application in which the ram 1 is of the kind termed anon-feed back ram, the branch conduit 37, the ports 35 and 36 and thesection of the conduit 38 extending from A-A in the figure is replacedby a conduit or duct B shown in dashed lines in the figure.

What we claim is:

1. A self-locking fluid-pressure-operated actuator, having a ramcylinder and a piston movable in said cylinder between a first and asecond relative position, a baulk element operatively connected to saidram to be moved from a first to a second position as said piston movesfrom said first to said second relative position and vice versa, a latchmember movable, when said baulk element is in its first position,between a locking position in which it prevents the baulk. member frommoving towards its second position, and a free position in which itpermits such movement of the baulk member, a looking ram operativelyconnected to the latch member and having a locking ram cylinder and apiston movable therein, a selector valve for connection to afluid-pressure supply, said valve being movable between a first positionin which it establishes connection between such supply and a firstservice line supplying fluid pressure to the locking ram for moving thelatch member to its free position, said first service line having abranch leading to one end of the main ram cylinder for permitting theadmission of fluid pressure to move the main ram piston to its saidfirst position, and a second position in which it establishes connectionbetween said supply and a second service line leading to the other endof the main ram cylinder, for permitting the admission of fluid pressureto move the main ram piston to its second position, said second serviceline having a branch leading to the locking ram cylinder for the supplythereto of fluid pressure to move the latch to said locking position,and said branch of the first service line including a cut-otf valvemeans operatively connected with the latch member to permit fluid topass through said branch of the first line only when the latch member isin said free position.

2. An actuator as claimed in claim 1, wherein the branch of said secondservice line includes a latch-locking valve means operatively connectedwith the baulk member to only permit passage of fluid through saidbranch of the second service line when said baulk member is in saidfirst position.

3. A self-locking pneumatic actuator, comprising a main ram cylinderhaving a peripheral wall and two end walls, a piston movable in saidcylinder between a first and a second position, output means including apiston rod attached to said piston and extending through a bore in oneof said end walls, a latch member movable into and out of a position oflocking engagement with said output means when said piston is in saidfirst and second position, latch-actuating means including a lockingcylinder having a peripheral wall and two end walls, a locking pistonmovable in said locking cylinder between a locking position in whichsaid latch member is in such locking engagement, and a free position,means operatively connecting the locking piston to the latch andincluding a locking-piston rod extending through a bore in one of theend walls of the locking cylinder, a wall having a bore through whichthe locking piston-rod passes, and having a passage so arranged as totraverse said bore thereof and be normally closed by the piston rod ofthe locking piston, a two-position selector valve having apressure-inlet port, a first and a second service port, and atmosphericport means, and a valve element for selectively connecting one of theservice ports to the inlet and the other to the atmospheric port meanswhen the selector valve is in one position and vice versa when theselector valve is in the other position, a first service line leadingfrom said first service port to one end of said locking cylinder for theadmission of fluid to efiect withdrawal of the latch, and also leadingfrom said first service port to one end of said passage, an actuatorline leading from the other end of said passage to one end of the maincylinder for the admission to said main cylinder of fluid to move themain piston to its second position, the piston rod of the locking pistonbeing provided with first port means which, when the locking piston isin the free position removes the closure of said passage, and a secondservice line having a first branch leading from the second service portto the main cylinder for supplying thereto fluid to move the main pistonto its first position and a second branch leading from said secondservice port to the locking cylinder for the supply of fluid to thelocking cylinder to urge the latch member to its locked position.

4. An actuator as claimed in claim 3 including a further wall having abore through which the main ram piston rod passes, said second branch ofthe second service passage extending through said further wall acrosssaid bore so as to be normally closed by said main-rain piston rod, saidmain ram piston rod having a port so arranged as to open said normallyclosed branch of the second passage in said further wall when the mainram piston is in its first position.

5. An actuator as claimed in claim 4, wherein said further wall isconstituted by said end wall of the main ram cylinder.

6. An actuator as claimed in claim 3, wherein said passage is arrangedin said end Wall of the locking-ram cylinder.

7. An actuator as claimed in claim 3, wherein the 15 6 locking pistonrod is provided with second port means which when the locking piston isin the locked position, vent that end of the passage which is connectedto the main cylinder by said first service line.

References Cited in the file of this patent UNITED STATES PATENTS1,085,964 Briggs Feb. 3, 1914 1,189,251 Harden July 4, 1916 2,130,618Gnavi Sept. 20, 1938 3,003,472 Ferris et al. Oct. 10, 1961 FOREIGNPATENTS 384,715 Germany Nov. 5, 1923

1. A SELF-LOCKING FLUID-PRESSURE-OPERATED ACTUATOR, HAVING A RAMCYLINDER AND A PISTON MOVABLE IN SAID CYLINDER BETWEEN A FIRST AND ASECOND RELATIVE POSITION, A BAULK ELEMENT OPERATIVELY CONNECTED TO SAIDRAM TO BE MOVED FROM A FIRST TO A SECOND POSITION AS SAID PISTON MOVESFROM SAID FIRST TO SAID SECOND RELATIVE POSITION AND VICE VERSA, A LATCHMEMBER MOVABLE, WHEN SAID BAULK ELEMENT IS IN ITS FIRST POSITION,BETWEEN A LOCKING POSITION IN WHICH IT PREVENTS THE BAULK MEMBER FROMMOVING TOWARDS ITS SECOND POSITION, AND A FREE POSITION IN WHICH ITPERMITS SUCH MOVEMENT OF THE BAULK MEMBER, A LOCKING RAM OPERATIVELYCONNECTED TO THE LATCH MEMBER AND HAVING A LOCKING RAM CYLINDER AND APISTON MOVABLE THEREIN, A SELECTOR VALVE FOR CONNECTION TO AFLUID-PRESSURE SUPPLY, SAID VALVE BEING MOVABLE BETWEEN A FIRST POSITIONIN WHICH IT ESTABLISHES CONNECTION BETWEEN SUCH SUPPLY AND A FIRSTSERVICE LINE SUPPLYING FLUID PRESSURE TO THE LOCKING RAM FOR MOVING THELATCH MEMBER TO ITS FREE POSITION, SAID FIRST SERVICE LINE HAVING ABRANCH LEADING TO ONE END OF THE MAIN RAM CYLINDER FOR PERMITTING THEADMISSION OF FLUID PRESSURE TO MOVE THE MAIN RAM PISTON TO ITS SAIDFIRST POSITION, AND A SECOND POSITION IN